feat(tui): add capability keyword shimmer

[testikun]

Problem

Closes #301. Capability keywords were highlighted with one static color, so the pre-submit affordance had no shimmer feedback.

Value

Authorized subagent/workflow keywords now receive a subtle animated lavender shimmer while preserving text, layout, authorization, and model context.

Approach

• Add a pure phase-driven truecolor renderer with static 256-color fallback.
• Advance the phase with a session-scoped 120ms timer and clean it up on shutdown.
• Keep highlighting gated by the existing shared capability classifier.
• Add focused renderer and fallback tests.

Validation

• Node 24 focused test: 6 passed.
• Biome lint: passed.
• TypeScript: passed.
• git diff --check: passed.
• Full bun run check / bun run test: unavailable in this environment because Bun is not installed.

Impact

No persisted state, model-visible context, tool surface, or capability semantics changed.

[tt-a1i]

Reviewed the exact head against current main, along both repository standards and issue #301 requirements. No P2 or higher issue confirmed. The change adds lavender animation to already-authorized capability keywords without changing text, classifier decisions, tools or model context. Focused renderer tests passed 6/6; current required CI is green and Git merge-tree reports a clean integration. Nonblocking: the 256-color fallback is static but still requests renders every 120 ms; avoiding those redundant ticks would improve efficiency. Product recommendation: optional polish, lower priority than Web observability. No native TUI visual acceptance or merge performed.